Web cutting control system

ABSTRACT

A web cutting control system controlling the speed of a rotary cutter for automatic, continuous and precise cutting of a web fed at a constant speed into predetermined lengths or on the marks on the web. Two transducers generate pulses the number of which corresponds to the web feed length and the rotating angle of the rotary cutter, respectively. Three sensors detect the marks on the web, the completion of cutting, and the arrival of the cutter blades, respectively, to control the flow of signals. A desired cutting length or the distance between the mark detection point and the point of completion of cutting is preset. A reversible counter receives the pulses from these two transducers and the difference signal between the preset value and a reference signal and performs reversible counting thereof, the result of which is used to control the speed of motor for the rotary cutter to bring its speed into synchronization with the web feed speed for accurate cutting.

The present invention relates to a control system which provides anautomatic, continuous and accurate cutting of a web of continuouslyconveyed cardboard or the like by means of a rotary cutter into constantlengths or at fixed positions without stopping the flow of web at theinstant of cutting, with the speed of the rotary cutting being broughtinto synchronization with the speed at which the web is being fed.

In the cutting of a web continuously fed at a constant speed intodesired lengths, the cutting length is usually adjusted by varying theperiod or interval at which the web is cut. One important problem hereis how to achieve complete synchronization of the cutter speed with theweb feed speed, thereby minimizing dimensional error of the cut lengths.

A conventional web cutting machine will be described by way of examplein connection with FIG. 1. The main shaft C if driven from main motor Athrough a reduction gearing having a belt B. The feed roller for the webis driven from the main shaft through a bevel gear D. The rotation ofthe main shaft C is also transmitted through a Reeves drive variablespeed mechanism E to a synchronous fly mechanism F, the output of whichis coupled to one roll of a rotary cutter G for sychronous drive withthe other roll thereof. The speed of the rotary cutter is controlled bymeans of a motor H connected to the regulating part of Reeves mechanismE and that of synchronous fly mechanism F.

The conventional system provides some degree of synchronization betweenthe web speed and the cutter speed since the rotation of the main shaftis transmitted both to the web feed roller and to the rotary cutterthrough these mechanisms. However, because of some slipping in theReeves mechanism E and the complexity of the mechanisms, there isinevitably some cutting error due to transmission error between theelements. High cutting accuracy can not, therefore, be expected. Becauseboth the Reeves mechanism and the synchronous fly mechanism aremechanical ones, the prior art system is slow to follow any change ofthe cutting length during operation, which results in substantial lossof material due to inaccurate cutting.

An object of the present invention is to provide a web cutting controlsystem which utilizes modern electronics technology to control the speedof the rotary cutter, thereby bringing it into complete synchronizationwith the web running speed before the instant of cutting to ensure thatthe web is cut accurately into predetermined lengths or at fixedpositions.

Another object of the present invention is to provide a web cuttingcontrol system which provides automatic, accurate and continuous cuttingof a continuously conveyed web into predetermined lengths withoutinterrupting the flow of web.

A further object of the present invention is to provide a control systemmaking it possible to cut a web precisely on the marks which have beenpre-printed thereon at a fixed or varying interval.

A still further object of the present invention is to provide a webcutting control system which facilitates the setting and change of thecutting length and permits such change even during operation.

The present invention consists in a web cutting control system whichmakes it possible to cut a web automatically, continuously andaccurately either into digitally preset lengths or on the marks putthereon beforehand. These and other objects and advantages of theinvention will become more apparent from the following description anddrawings, in which:

FIG. 1 is a schematic illustration showing the operating principle of aconventional web cutting machine;

FIG. 2 is a schematic illustration, similar to FIG. 1, showing theoperating principle of a web cutting control system embodying thepresent invention;

FIG. 3 is a schematic illustration showing the mounting position ofthree sensors relative to the rotary cutter;

FIG. 4 is a side view of the rotary cutter provided with the controlsystem embodying the present invention;

FIG. 5 is front view of the rotary cutter of FIG. 4;

FIG. 6 is a block diagram of the control system embodying the presentinvention;

FIGS. 7a and 7b are wave form diagrams showing how the distance betweenthe marks on the web is discriminated to be "long-size" or "short-size"in the fixed-position cutting.

FIGS. 8-12 are graphs showing how various signals change and are countedin each cutting cycle for fixed-position cutting; and

FIGS. 13-20 are similar graphs showing the same for constant-sizecutting. The mechanical and electrical arrangements of a preferredembodiment of the present invention are shown in FIGS. 2-6.

A rotary cutter 3 has a pair of rolls coupled together by a pair ofgears 1 and 2 for synchronous rotation. (FIG. 2) The main shaft 4 of thelower roll is provided with a reduction gearing 5 to which is coupled aDC motor 6. A tachometer generator 7 and a transducer PG_(B) areconnected to the other end of the DC motor 6 to detect the rotatingangle of the rotary cutter 3. If the reduction gearing 5 has a reductionratio of 4:1, for example, the rotary cutter 3 makes one revolution foreach four revolutions of the motor 6. The transducer PG_(B), coupleddirectly to the motor 6, generates two different pulse sequences 90° outof phase from each other each at a rate of 600 pulses for eachrevolution thereof.

A wheel 8 is kept in contact with the web X to be cut with a sufficientpressure to be driven by friction. To the shaft 9 of the wheel 8 iscoupled a transducer PG_(A) to detect the length of the web which hasbeen fed. The transducer PG_(A), too, supplies two different pulsesequences 90° out of phase from each other each at a rate of 3000 pulsesfor each revolution thereof.

As shown in FIG. 3, a sensor OP_(A) (photoelectric tube) is provided ata distance l₃ ahead of the cutting point P to detect the cutting markswhich have been pre-printed on the web at predetermined or varyingspacings in fixed-position cutting.

Another sensor OP_(C) is provided at a position where the cutting bladeshave moved a peripheral distance L₁ mm past the actual cutting point inthe rotating direction, to detect completion of cutting and produce aweb cutting completion signal C.

The reason why the sensor OP_(C) for producing the cutting completionsignal C is located not at the actual cutting point P but at l₁ mm pastthe point P (FIG. 3) is that if the cutter 3 were stopped simultaneouslyupon completion of cutting, it would have its blades caught in the web.In order to avoid this, the cutter 3 is designed to stop only after ifhas cut the web and through an additional angle.

Also, at a peripheral distance l₂ mm of the cutting point P along theperiphery of the cutter 3 is located a third sensor OP_(B) to detect thearrival of the tip of cutter blade to produce a mark distancediscrimination signal.

Referring to FIGS. 4 and 5, the numeral 10 designates a frame; 11 arebearings for the rotary cutter 3; 12 is a cover for the gearing 5; 13 isa blower for cooling the motor 6; 14 are web feed rollers; and 15 is afluid pressure cylinder for the wheel 8. The pressure at which the wheel8 is pressed against the web X can be adjusted by means of the cylinder15.

Referring to the block diagram of the control system shown in FIG. 6, acomparison unit 16 compares the value L₀ preset on the cutting lengthsetter LA (digital switch) with the value B₀ preset on the referencepulse setter LB and feeds the difference therebetween (L₀ -B₀ =L), ifany, to a counting circuit described later. The comparison unit 16includes a reversible counter C₁ which counts the preset value L₀ fromthe cutting length setter LA, the comparator A₁ which compares thecontent L₀ of the counter C₁ with the value B₀ from the reference pulsesetter LB to give any difference therebetween, and a gate G_(E) E passesthe difference signal in synchronization with the pulses from the pulsegenerator OSC. On the cutting length setter LA is set a desired cuttinglength in millimeters for constant-size cutting, or the distance betweenthe cutting complete detection point and the mark detection point, thatis, l₁ +l₃ mm (FIG. 3) for fixed-position cutting. On the referencepulse setter LB is set the number of pulses indicative of thecircumference of the rotary cutter 3.

The numeral 17 designates an addition/subtraction discriminating circuitwhich compares the two preset values and couples the differencetherebetween to the addition or subtraction input of the reversiblecounter C₁ according to the result of the comparison. This circuit 17includes a comparator A₂ which compares the preset value L₀ from thecutting length setter LA with the preset value B₀ from the referencepulse setter LB to give an addition or subtraction command signal to agate G_(D) according to the result of comparison, and the gate G_(D)which couples the signal fed from the gate G_(E) back to the addition orsubtraction input of the counter C₁ in response to the command signalfrom the comparator A₂.

A web flow detection circuit 18 detects the length of the web which hasbeen fed to generate pulses, the number of which corresponds to thelength. The circuit 18 includes the transducer PG_(A) coupled to thewheel 8 in contact with the web, a pulse amplifier PA₁ for amplifyingthe pulses generated by the transducer PG_(A), a phase discriminatingcircuit B₁ for discriminating the rotating direction of the transducerPG_(A), and a constant multiplier D₁ which multiplies the number ofpulses by a constant.

The generation of pulses from the circuit 18 is accomplished in thefollowing manner in the preferred embodiment. As described above, thetransducer PG_(A) supplies two different pulse sequences 90° out ofphase from each other, each at a rate of 3,000 pulses for eachrevolution thereof. Since the wheel 8 has a circumference of 1,200 mm,the web runs for 1,200 mm while the wheel 8 makes one revolution. Inorder to generate pulses at a rate of one pulse for each 0.1 mm of theweb length, the two pulse sequences are combined and [(3000+3000)×2]amplifier PA₁ and the phase discriminating circuit B₁. Thus, pulses,φ_(A), are supplied from the constant multiplier D₁ at a rate of 12,000pulses for each revolution of the wheel 8 as a signal indicative of theweb feed length.

A cutter rotating angle detection circuit 19 includes the transducerPG_(B) coupled to the motor 6, a pulse amplifier PA₂ a phasediscriminating circuit B₂ and a constant multiplier D₂. In the preferredembodiment the constant multiplier D₂ is set as follows: Because of thegear ratio of 4:1, the rotary cutter 3 makes one revolution for eachfour revolutions of the motor 6 and thus the transducer PG_(B). Sincethe rotary cutter 3 has a circumference of 864 mm, 8,640 pulses arerequired for each revolution thereof to produce pulses at the rate ofone pulse for each 0.1 mm. For this purpose, two pulse sequences fedfrom the transducer PG_(B) each at a rate of 600 pulses per revolutionthereof are electrically combined and doubled as follows:

    (600 PPR+600 PPR)×2=2,400 PPR

Thus, the number of pulses generated for four revolutions of thetransducer PG_(B) are 2,400 PPR×4=9,600 PPR. The constant multiplier D₂is set at 0.9 to convert this rate to 8,640 pulses per revolution of thecutter (8,640/9,600=0.9). Thus, 8,640 pulses produced as φ_(B) each timethe transducer PG_(B) makes four revolutions and the rotary cutter 3makes one revolution.

The circuit configuration for fixed-position cutting will now bedescribed. In this mode of cutting, the input signal (from afixed-position cutting selector switch P.P) to the interface I₁ is kepton.

First, it will be explained how the distance between the marks isdiscriminated to be long-size or short-size. The logic fordiscrimination is which first comes, the mark detection signal A or thecutting completion signal C, after the mark distance discriminationsignal B has arrived. To put this in another way, any length longer orshorter than l₁ +l₃ (=L₀) is discriminated to be long-size andshort-size, respectively.

If first a cutting completion signal C and then a mark detection signalA comes after a mark distance discrimination signal B has been given asshown at (a) in FIG. 7, the control system will operate in the long-sizecutting mode, in which an input signal discriminating circuit H₀supplies signal α₁ to close the gate G_(A) throughout from thecompletion of cutting to the detection of the next mark. Thus, only thesignal φ_(B) is stored in the reversible counter C₂ as a positive signalwhile signal φ_(A) is blocked at gate G_(A). When a mark detectionsignal A comes from the sensor OP_(A), the input signal discriminatingcircuit H₀ momentarily supplies signal α₂ and resets signal α₁ to openthe gate G_(A).

If first a mark detection signal A and then a cutting completion signalC are received after signal B, the control system will operate in theshort-size cutting mode as shown at (b) in FIG. 7. In this mode, with amark detection signal A, the input discriminating circuit H₀ suppliessignal α₂ momentarily. From the arrival of a mark detection signal A tothat of a cutting complete signal C, it also supplies signals α₄ and α₃to keep the gate G_(C) open and the gate G_(B) closed, respectively.With a cutting completion signal C, signals α₄ and α₃ are reset to closethe gate G_(C) and open the gate G_(B).

The fixed-position cutting by the long-size cutting mode will be firstdescribed. When the interface I₁ receives a mark detection signal A fromthe sensor OP_(A), the input discriminating circuit H₀ supplies a presetsignal α₂ to cause the reversible counter C₁ to store a value L₀ (l₃mm+l₁ mm) preset on the cutting length setter LA. The value L₀ iscompared by the comparator A₁ with the value B₀ (indicative of thecircumference of the cutter 3) preset on the reference pulse setter LB.When L₀ -B₀ becomes negative, the output of the comparator A₁ passesthrough the gates G_(E) and G_(B) in synchronization with the pulse froma reference pulse generator OSC. (The gate G_(E) is designed to openwhen the output from the comparator A₁ is other than zero, and closeonly when it is zero.) It is a fed through the synchronizer SN to thegates G_(D) and G_(F).

On the other hand the comparator A₂ also compares L₀ with B₀ and sends acommand to couple the output of gate G_(D) to the addition input of thereversible counter C₁ as long as L₀ -B₀ <0, to feed the signal from thegates G_(E) and G_(B) back to the reversible counter C₁ to add it to thevalue L₀ stored therein.

As soon as the output from the comparator A₁ becomes zero, the gateG_(E) closes to stop the signal fed back to the counter C₁. This meansthat the remainder L(L=L₀ -_(BO)) has been obtained by subtraction ofthe value B₀ indicative of the circumference of rotary cutter 3 from thepreset value L₀.

The remainder thus obtained goes through the synchronizer SN to the gateG_(F) which directs it through the OR gate G_(J) to the reversiblecounter C₂ as a signal to be subtracted in coincidence with the signalfed from the comparator A₂ on the condition that L₀ -B₀ <0.

Also, the output pulse φ_(A) from the web flow detection circuit 18 isfed through the synchronizer SN, gate G_(A) and OR gate G_(J) to thereversible counter C₂ as a signal to be subtracted. As shown in FIG. 8,the reversible counter C₂ thus receives these two signals every minuteboth as a subtraction signal to obtain L-φ_(A). On the other hand, assoon as one cutting operation is complete, pulses φ_(B) the number ofwhich is proportional to the angle for which the rotary cutter 3 hasrotated from the cutting completion detection point are applied as asignal to be added to the counter C₂ through the synchronizer SN and theOR gate G_(I). Thus, the counter C₂ performs the following operation orreversible counting:

    (L-φ.sub.A)+φ.sub.B, or (L.sub.0 -B.sub.0)-φ.sub.A +φ.sub.B

These inputs are combined by the counter C₂ as graphically shown in FIG.8, in which the arrows AD and SU indicate the addition and subtractiondirections, respectively. Also, MP stands for the mark detection pointand CP for the point where one cutting operation has been justcompleted. (These designations are used with the same meaning in all ofthe similar figures.)

The result of operation by the reversible counter C₂ is fed moment bymoment through a digital/analog converter D/A to a function generator FGwhich outputs voltage, V_(C), shown in FIG. 9-a,

    V.sub.C =ƒ(R)=ƒ[(L.sub.0 -B.sub.0)-φ.sub.A +φ.sub.B ]

As shown in FIG. 9-b, the output voltage V_(C) is coupled to theoperational amplifier OP which compares it with a voltage V_(A) todetermine the differential, V₀ =V_(A) -V_(C). The voltage V_(A) comesfrom a frequency-voltage converter F/V to which is fed pulse signalφ_(1A) proportional to the web running speed.

The output voltage V₀ is applied to the comparator A₃ to compare it with0 volt to discriminate whether V₀ =V_(A) -V_(C) <0 or ≧O. Because V_(C)is negative in this mode, V₀ =V_(A) -(-V_(C))=V_(A) +V_(C) >0.Therefore, the voltage V₀ is fed through the make contact CR_(a) of therelay CR to the motor control circuit CO so that the DC motor 6 isaccelerated.

As the equation V₀ =V_(A) +V_(C) shows, the DC motor 6 rotates at ahigher speed than the web feed speed by a value corresponding to V_(C).Therefore, the input signal, φ_(B), the reversible counter C₂ increasesat a higher rathe than φ_(A) as shown in FIG. 8, although the former isa signal to be added and the latter a signal to be subtracted.

At the point SS in FIG. 9-b where V_(C) =(L₀ -B₀)-φ_(A) +φ_(B) =0, thatis, V₀ =V_(A), the speed of the rotary cutter 3 comes into completesynchronization with the web feed speed with the next mark and thecutter blades aqually spaced away from the cutting point. The web andthe cutter move on in this condition unless there is any change in theweb feed speed and the cutter speed, so that the web will be cutprecisely on the mark. The graphs in FIGS. 8, 9-a and 9-b are summarizedin FIG. 10.

If the speed of the DC motor 6 for the rotary cutter 3 should become sohigh that (L₀ -B₀)-φ_(A) +φ_(B) is not zero any more but becomespositive, the speed command voltage V₀ (=V_(A) -V_(C)) fed to the motorcontrol circuit CO would not be equal to V_(A) any more, but becomesmaller than V_(A) proportional to the web speed. This means that the DCmotor 6 decelerates until V_(C) decreases to zero again.

Also, if the web feed speed should decrease, for example, φ_(A) wouldnot increase so much as φ_(B) and (L₀ -B₀)-φ_(A) +φ_(B) and thus theoutput voltage V_(C) would become positive with the voltage V_(A) onceagain, which means that the speed of the rotary cutter 3 comes intosynchronization with the web feed speed.

Upon completion of one cutting operation, a cutting completion signal Cfrom the sensor OP_(C) is fed into the interface I₁. Simultaneously, theinput discriminating circuit H₀ supplies signal α₁ to close the gateG_(A) to cut off the pulses φ_(A) from the web flow detection circuit18, and forcibly make inoperative the relay CR in the comparator A₃ torestore the break contact CR_(b) thereof to its open position.

Accordingly, the motor control circuit CO is connected to zero voltagethrough the delay circuit CT so that the motor 6 stops after a certaintime. The rotary cutter 3 remains stopped until the next mark detectionsignal A arrives. The angle of rotation of the rotary cutter 3 from thecompletion of cutting to the actual stop thereof is stored in thereversible counter C₂ as signal φ_(B) from the cutter rotating angledetection circuit 19.

The cutting cycle in the fixed-position cutting is illustrated by line fat a in FIG. 7, in which the vertical dotted lines show the cuttingpoints. When the horizontal dotted line SL is reached, the cutter speedcomes into synchronization with the web speed. At the level of solidline CL, the rotary cutter 3 stops. The graph shows that the rotarycutter 3 is intermittently operated in the long-size cutting mode.

Next, cutting control in the short-size cutting mode will be describedwhere the mark detection signal A is followed by the cutting completionsignal C as shown at b in FIG. 7. In this mode, signal flow in thecontrol system is almost the same as in the long-size cutting modeexcept for the output signals from the input discriminating circuit H₀and the operation of the gates G_(B) and G_(C) responsive thereto. Whenthe interface I₁ receives first a mark detection signal A from thesensor OP_(A) after it has received a mark distance discriminatingsignal B from the sensor OP_(B) the input discriminating circuit H₀produces preset signals α₂, α₃ and α₄. With signal α₂, the value L₀preset on the setter LA is registered in the reversible counter C₁through the interface I₂. Also, signal α₄ opens the gate G_(C) andsignal α₃ closes the gate G_(B).

From the value L₀ stored in the counter C₁ is subtracted the pulsesφ_(A) fed through the gate G_(C) from the web flow detection circuit 18until the web is cut on the last mark and the cutting completion signalC comes into the system.

In other words, if the next mark is detected by the sensor OP_(A) beforethe web cutting on the last mark is complete, the distance between themarks is discriminated to be less than l₁ +l₃ mm shown in FIG. 3. Withsignal A from the sensor OP_(A), the reversible counter C₁ is set tosubtract from the preset value L₀ the length α which the web has runbefore the cutting completion signal C for the last mark enters. Byperforming this subtraction, the control system judges the web cuttingsize to be not L₀ but Z(=L₀ -α), the value Z being left in the counterC₁.

During the subtraction operation, the result of subtraction is not fedto the reversible counter C₂ because the gate G_(B) has been closed bysignal α₃. The pulses φ_(A) and φ_(B) also continue to be fed to thecunter C₂ through the gate G_(A) and OR gate G_(J), and the OR gateG_(I), respectively.

When the cutting completion signal C arrives from the sensor OP_(C), thesignals α₃ and α₄ from the input discriminating circuit H₀ disappear sothat the gate G_(B) opens whereas the gate G_(C) closes. Operationthereafter is the same as in the long-size cutting mode except that thedifference signal Z-B₀, not L₀ -B₀, is fed through the gate G_(F).

In the short-size cutting mode, the rotary cutter 3 continues to bedriven at a speed equal to, or higher than, the web feed speed withoutintermittent stop as shown in line f' at b in FIG. 7. Speed control inthe short-size cutting mode is graphically illustrated in FIGS. 11 and12.

Constant-size cutting, another object of the present invention, will nowbe described.

In this control mode, the fixed-position cutting selector switch P.P,coupled to the interface I₁, is placed in its OFF position to shut outthe signals A and B from the sensors OP_(A) and OP_(B) to keep the gatesG_(A) G_(B) opened and the gate G_(C) closed. Also, the web need nothave marks placed thereon.

First, speed control will be explained in the case where the value L₀preset on the cutting length setter LA is larger than, or equal to, thevalue B₀ on the reference pulse setter LB (L₀ ≧B₀). (In constant-sizecutting, any desired cutting length may be set as L₀ on the cuttinglength setter LA, through L₀ =l₁ +l₃ mm in fixed-position cutting.)

Upon completion of cutting, the input discriminating circuit H₀ suppliessignal α₂ in response to signal C from the sensor OP_(C). With signal α₂the preset value L₀ on the cutting length setter LA is stored in thereversible counter C₁ through the interface I₂. The value L₀ is comparedby the comparator A₁ with the value B₀ preset on the reference pulsesetter LB. Since L₀ -B₀ >0 the gate G_(E), to which is coupled the pulsegenerator OSC, opens to pass the output of the comparator A₁ to the gateG_(B) in synchronization with the pulse from the reference generatorOSC.

On the other hand, the comparator A₂ also compares L₀ with B₀ to couplethe output of the gate G_(D) to the subtraction input of the reversiblecounter C₁ while L₀ -B₀ ≧0 to feed the output from the gate G_(E) backto the counter C₁ to subtract it from the content thereof. In time, L₀--B₀ will become zero so that the gate G_(E) closes to stop the feedbacksignal for subtraction. This means that in the meantime, the differencesignal L=L₀ -B₀ has been fed through the gates G_(E) and G_(B) towardthe counter C₂. It is fed from these gates through the synchronizer SNto the gate G_(F), which in response to the signal fed from thecomparator A₂ on the condition that L₀ -B₀ ≧0 directs it through the ORgate G₁ into the reversible counter C₂ as a signal to be added.

On the other hand, the pulses φ_(A) from the web flow detection circuit18 are applied through the synchronizer SN, gate G_(A) and OR gate G_(J)to the counter C₂ as a signal to be subtracted. They are fed at a rateof one pulse for each 0.1 mm of web length as described above. Also, asthe rotary cutter 3 rotates, the pulses φ_(B) corresponding to therotating angle thereof from the cutting completion point are suppliedthrough the synchronizer SN and the OR gate G₁ to the counter C₂ as asignal to be added. Thus, the counter C₂ performs the followingoperation or reversible counting: (L₀ -B₀)-φ_(A) +φ_(B).

These inputs are synthesized in the counter C₂ as graphicallyillustrated in FIG. 13.

The result of operation by the counter C₂ is fed by the minute throughthe digital/analog converter D/A to the function generator FG, theoutput of which V_(C) =ƒ(R)=ƒ[(L₀ -B₀)-φ_(A) +φ_(B) ] is shown in FIG.14.

As in fixed-position cutting, the output voltage V_(C) is applied to theoperational amplifier OP, which determines the differential V₀ betweenit and voltage V_(A) from the frequency/voltage converter F/V (V₀ =V_(A)-V_(C)).

The resultant output voltage V₀ is fed to the comparator A₃ to compareit with 0 volts to discriminate whether V₀ =V_(A) -V_(C) <0 or ≧0. If V₀is negative, the relay CR will not be actuated with the make contactCR.sub.α open as shown in FIG. 6 to block the input to the motor controlcircuit CO. If V₀ is positive, the relay CR will be actuated, the makecontact CR.sub.α being closed to input the voltage V₀ from theoperational amplifier OP to the motor control circuit CO.

Since L₀ -B₀ is positive and thus the voltage V_(C) is larger than V_(A)at the cutting completion point, the output of the operational amplifierOP (V₀ =V_(A) -V_(C)) is negative so that the DC motor 6 is atstandstill. As the web further runs with pulses φ_(A) increasing, theoutput, V_(C), from the frequency generator FG decreases until itbecomes equal to V_(A) and thus V₀ becomes zero (FIG. 15), when therelay CR is actuated.

From then on, the motor 6 is made to run through the control circuit COto drive the rotary cutter 3, pulses φ_(B) corresponding to the rotatingangle thereof being fed again from the rotating angle detection circuit19 through the synchronizer SN and the OR gate G_(t) to the reversiblecounter C₂ as an addition signal. Since the pulses φ_(B) are smaller innumber than the pulses φ_(A) indicative of the web feed length at thisearly stage, the output voltage V₀ from the operational amplifier OPincreases to accelerate the DC motor 6 rapidly until the cutter speedfollows the web feed speed.

At the point where (L₀ -B₀)-φ_(A) +φ_(B) becomes zero, the rotary cutterspeed will come into complete synchronization with the web feed speedwith the cutter blades and the point of the web at which it is to be cutequally spaced from the cutting point. This condition remains unchangedunless there is any further change in the cutter speed or the web speed,so that the web is cut into a predetermined size L₀. FIG. 16 summarizesthe graphs shown in FIGS. 13 to 15.

If there should be any change in the cutter or web speed, the cutterwill be brought back to synchronization with the web feed speed in quitethe same manner as in fixed-position cutting.

The manner in which the cutter speed is controlled will not be describedin the case where the preset value L₀ on the cutting length setter LA issmaller than the preset value B₀ on the reference pulse setter LB (L₀-B₀ <0).

In this case, too, signal flow in the control system is almost the sameas in the above-mentioned case (L₀ -B₀ ≧0), but the gates G_(D) andG_(F) operate differently according to the result of discrimination bythe comparator A₂.

With signal α₂, the preset value L₀ on the cutting length setter LA isstored in the reversible counter C₁ through the interface I₂. Thecomparator A₁ compares L₀ with B₀ to discriminate L₀ -B₀ <0.Accordingly, the gate G_(E) opens to pass the output of the comparatorA₁ to the gate G_(B) in sychronization with the pulse from the referencegenerator OSC.

On the other hand, the comparator A₂ also compares L₀ with B₀ to couplethe output of the gate G_(D) to the addition input of the reversiblecounter C₁ while L₀ -B₀ <0 to feed the signal from the gate G_(E) backto the counter C₁ to add it to value L₀ therein. In time, L₀ -B₀ becomeszero so that the gate G_(E) closes to stop the feedback signal foraddition. This means that the difference signal L=L₀ -B₀ has been fedfrom the gates G_(E) and G_(B) toward the counter C₂. It is fed fromthese gates through the synchronizer SN to the gate G_(F) which inresponse to the signal fed from the comparator A₂ on the condition thatL₀ -B₀ <0 directs it through the OR gate G_(J) into the reversiblecounter C₂ as a signal to be subtracted.

In the meantime, as in the case where L₀ -B₀ ≧0, pulses φ_(A) from theweb flow detection circuit 18 are supplied to the counter C₂ as asubtraction signal, and pulses φ_(B) rom the rotating angle detectioncircuit 19 as a addition signal. Thus, the counter C₂ performs thefollowing operation: (L₀ -B₀)-φ_(A) +φ_(B).

As in the above described case, the result of operation by the counterC₂ is fed by the minute through the digital/analog converter D/A and thefunction generator FG to the operational amplifier OP, the output V₀ ofwhich is compared with volts at the comparator A₃.

Because V_(C) is negative in this case, V₀ =V_(A) -(-V_(C))=V_(A)+V_(C) >0. Therefore, the voltage V₀ is applied through the make contactCR.sub.α of the relay CR to the motor control circuit CO to acceleratethe DC motor 6. As the equation V₀ =V_(A) +V_(C) shows, the DC motor 6rotates at a higher speed than the web feed speed by V_(C). Therefore,the input signal, φ_(B), to the reversible counter C₂ increases at ahigher rate than φ_(A) as shown in FIG. 17, although the former is asignal to be added and the latter a signal to be subtracted.

At the point SS in FIG. 19 where V_(C) =(L₀ -B₀)-φ_(A) +φ_(B) =0, thatis, V₀ =V_(A), the speed of the rotary cutter 3 comes into completesynchronization with the web feed speed with the cutter blades and thepoint at which the web is to be cut equally away from the cutting point.The rest is the same as in the above described case (L₀ -B₀ ≧0). Thegraphs in FIGS. 17 to 19 are summarized in FIG. 20.

The present invention makes possible continuous, automatic cutting ofthe web on the marks thereon or into predetermined lengths by means ofthe abovementioned arrangement. The control system embodying the presentinvention has the following advantages over the conventional controlsystems described at the beginning of the specification:

1. The length into which the web is to be cut is manually set on adigital switch. This setting may be readily and instantaneously changedeven during operation without producing any appreciable material loss.

2. Electronic control by means of digital and analog control systemsprovides high accuracy with a minimum of cutting error and makespossible control of the cutting length setting by any external signal(from an electronic computer, for example).

3. The speed of a rotary cutter used is electronically brought intosynchronization with the web feed speed and kept in such a state untilthe instant of cutting. This assures not cutting error and provides anextremely simple mechanical arrangement compared with the prior artsystem in which this synchronization was achieved by mechanical means.Directly coupled to a DC motor through a gearing, the rotary cutter hasa driving which is very simple in construction.

4. The web is cut by detecting the marks pre-printed thereon by means ofa mark detection sensor. Therefore, independently of the size betweenthe marks, the web is cut precisely on the marks.

5. If there should arise any change in the web feed speed, the controlsystem causes the rotary cutter to follow it automatically because theweb feed speed is converted to a voltage for use as a reference voltage.Such a change cannot, therefore, interfere with precise cutting.

6. The electronic control system with extremely simple mechanicalconstruction provides noiseless, stable cutting control.

7. Three sensors are provided to discriminate the distance between themarks to be long-size or short size according to the order in whichsignals come thereform. This assures that independently of the distancebetween the marks, the web is precisely cut on the marks.

What is claimed is:
 1. A control system for cutting a web fed .[.at aconstant-speed.]. by means of a rotary cutter driven by a motorselectively either into predetermined lengths or at fixed positionsthereof, said control system comprising in combination:a. firsttransducer for generating pulses, the number thereof being proportionalto the length of the web which has been fed; b. a second transducer forgenerating pulses, the number thereof being proportional to the anglethrough which said rotary cutter has rotated; c. a first setting meansfor setting reference pulses, the number thereof being predetermined bya fixed rotating angle of said rotary cutter; d. a first sensor fordetecting the marks put beforehand on the web to give a mark detectionsignal, e. a second sensor for detecting completion of each cuttingoperation to give a cutting completion detection signal; f. a thirdsensor for giving a mark distance discriminating signal fordiscrimination whether the detection of the next mark occurs before orafter the completion of cutting on the last mark; g. a second settingmeans for digitally setting selectively either a desired cutting lengthor the distance between the mark detection point and the cuttingcompletion detection point; h. a first reversible counting meansresponsive to a detection signal from said first sensor for counting anydifference between the value preset on said first setting means and thevalue preset on said second setting means; i. an addition/subtractiondiscriminating means for comparing the value from said first settingmeans with the value from said second setting means to couple saiddifference between said two values to said first reversible countingmeans as a signal to be added or a signal to be subtracted according tothe result of comparison; j. .[.said first.]. .Iadd.a second.Iaddend.reversible counting means receiving the pulses from said firsttransducer as a signal to be subtracted and the pulses from said secondtransducer as a signal to be added as well as the difference betweensaid two values and performing reversible counting thereof; k. a.[.differentiating.]. .Iadd.differencing .Iaddend.means for obtainingany difference between the result of said reversible counting by said.[.first.]. .Iadd.second .Iaddend.reversible counting means and avoltage proportional to the web feed speed; l. a motor speed controlmeans for discriminating the polarity of the output voltage from said.[.differentiating.]. .Iadd.differencing .Iaddend.means and controllingthe speed of the motor for driving the rotary cutter according to thepolarity and quantity of said output voltage; and m. .[.a second.]..Iadd.said first .Iaddend.reversible counting means .Iadd.further being.Iaddend.for subtracting from the preset value on said .[.firstsensing.]. .Iadd.second setting .Iaddend.means a value corresponding tothe length of the web which has been fed from the instant of detectionby said first sensor to the instant of detection by said second sensor,in case the mark detection signal from said first sensor arrives.[.inn.]. .Iadd.in .Iaddend.advance of the cutting completion detectionsignal from said second sensor after the mark distance discriminatingsignal has come from said third sensor. .Iadd.
 2. A control system forcontrolling the cutting of a web into predetermined lengths by means ofa rotary cutter driven by a motor; said control system comprising incombination; (a) a first transducer means for generating pulses, thenumber thereof being proportional to the length of the web which hasbeen fed; (b) a signal generator means for generating a signalproportional to the web speed; (c) a second transducer means forgenerating pulses, the number thereof being proportional to the anglethrough which said rotary cutter has rotated; (d) means for providing afirst reference value, the magnitude thereof being related to the sweptcircumference of said rotary cutter; (e) a sensor for establishing aknife position datum signal during each cutting cycle; (f) a settingmeans for providing a second value representative of a desiredpredetermined cutting length; (g) a combining means for combining saidfirst and second values for obtaining a third value representative ofthe difference therebetween; (h) a reversible counting means whichreceives the third value from said combining means in response to eachdatum signal and which subtracts therefrom the pulses from said firsttransducer means and adds thereto the pulses from said second transducermeans to achieve a resultant count and producing a signal proportionalto the resultant count; (i) a differencing means for obtaining a signalproportional to any difference between said signal proportional to saidresultant count and said signal proportional to the web speed; and (j)motor control means responsive to the signal from said differencingmeans for controlling the operation of the motor to cut the web intosaid predetermined lengths. .Iaddend..Iadd.
 3. A control system asclaimed in claim 2 which is also capable of controlling the rotarycutter for cutting the web at points according to preapplied marks onthe web, further comprising: (a) a further sensor for detecting marks onthe web at which the web is to be cut and for giving a mark detectionsignal; said setting means having means for providing the second valuewhich, when the system is operating to cut the web at points accordingto preapplied marks on the web, provides the second value having amagnitude being determined by the distance between the mark detectionpoint and the knife position datum detection point, said distance beinga distance from said mark detection point and measured along the path ofweb travel and around the swept circumference of the cutter to aposition which lies in the range from the cutting point to a pointspaced around the swept circumference of the cutter from said cuttingpoint; said combining means having means which, when the system isoperating to cut the web at points according to preapplied marks on theweb, (1) when said further sensor detects a mark according to which acut is to be made no earlier than the occurrence of the knife positiondatum signal for the next preceding cut, operates in a long-size modefor combining said first and second values to provide a third valuerepresentative of the difference between said first and second values,and (2) when said further sensor detects a mark according to which a cutis to be made before the occurrence of the knife position datum signalfor the next preceding cut, operates in a short-size mode for combiningsaid first value, said second value and a value corresponding to thelength of web which has been fed from the instant of detection by saidfurther sensor to the occurrence of the knife position datum signal forobtaining the difference between the first and second values reduced bysaid value corresponding to the length of fed web to obtain a thirdvalue; said reversible counting means having means which, when thesystem is operating to cut the web at points according to preappliedmarks on the web, (1) when said combining means operates in saidlong-size mode, during each cutting cycle receives said third value andwhich receives pulses from said second transducer means as a signal tobe added and which on generation of a mark detection signal by saidfurther sensor receives pulses from said first transducer means as asignal to be subtracted to achieve a resultant count and producing asignal porportional to said resultant count, and (2) when said combiningmeans operates in said short-sized mode, on generation of each datumsignal by said firstmentioned sensor receives said third value and whichalso receives pulses from said second transducer means as a signal to beadded and pulses from said first transducer means as a signal to besubtracted to achieve a resultant count and producing a signalproportional to said resultant count. .Iaddend..Iadd.
 4. A controlsystem as claimed in claim 3 further comprising more sensing means fordetermining whether the detection of a mark occurs before or after theoccurrence of said knife position datum signal for the next precedingmark and for controlling the operation of said combining means and saidreversible counting means in the appropriate one of said long-size modeand said short-size mode. .Iaddend..Iadd.
 5. A control system forcontrolling the cutting of a web at points according to preapplied marksthereon by means of a rotary cutter driven by a motor, comprising: (a) afirst sensor for detecting marks on the web at which the web is to becut and giving a mark detection signal; (b) a second sensor forestablishing a knife position datum signal during each cutting cycle,the distance between consecutive marks being greater than the distancebetween said first sensor and said second sensor, the latter distancebeing a distance from said first sensor and measured along the path ofthe web and around the swept circumference of the cutter to a positionwhich lies in the range from the cutting point to a point spaced aroundthe swept circumference of the cutter from said cutting point; (c) afirst transducer means for generating pulses, the number thereof beingproportional to the length of the web which has been fed; (d) a signalgenerator means for generating a signal proportional to the web speed;(e) a second transducer means for generating pulses, the number thereofbeing proportional to the angle through which said rotary cutter hasrotated; (f) a first means for providing a first reference value, themagnitude thereof being related to the swept circumference of saidrotary cutter; (g) a second means for providing a second value, themagnitude thereof being determined by the distance between the markdetection point and the knife position datum detection point; (h) acombining means for combining said first and second values for providinga third value representative of the difference therebetween; (i) areversible counting means which, during each cutting cycle, receivessaid third value and which receives pulses from said second transducermeans as a signal to be added and which on generation of a markdetection signal by said first sensor receives pulses from said firsttransducer means as a signal to be subtracted to achieve a resultantcount and producing a signal proportional to said resultant count; (j) adifferencing means for obtaining a signal proportional to any differencebetween said signal proportional to said resultant count and said signalproportional to the web speed; and (k) motor control means responsive tothe signal from said differencing means for controlling the operation ofsaid motor to cut the web on said marks. .Iaddend..Iadd.
 6. A controlsystem as claimed in claim 5 in which the distance between consecutivemarks can also be less than the distance between said first sensor andsaid second sensor, andsaid combining means, when the first sensordetects a mark according to which a cut is to be made no earlier thanthe occurrence of the knife position datum signal for the next precedingcut, operating in a long-size mode for combining said first and secondvalues to provide the third value representative of the differencebetween said first and second values, and further having means which,when the first sensor detects a mark according to which a cut is to bemade before the occurrence of the knife position datum signal for thenext preceding cut, operates in a short-size mode for combining saidfirst value, said second value and a value corresponding to the lengthof web which has been fed from the instant of detection by said firstsensor to the occurrence of the knife position datum signal forobtaining the difference between the first and second values reduced bysaid value corresponding to the length of fed web to obtain a thirdvalue; said reversible counting means when said combining means operatesin said long-size mode, during each cutting cycle receives said thirdvalue and which receives pulses from said second transducer means as asignal to be added and which on generation of a mark detection signal bysaid first sensor receives pulses from said first transducer means as asignal to be subtracted to achieve a resultant count and producing asignal proportional to said resultant count, and further having meanswhich, when said combining means operates in said short-size mode, ongeneration of each datum signal by said second sensor receives saidthird value and which also receives pulses from said second transducermeans as a signal to be added and pulses from said first transducermeans as a signal to be subtracted to achieve a resultant count andproducing a signal proportional to said resultant count. .Iaddend..Iadd.7. A control system as claimed in claim 6 further comprising modesensing means for determining whether the detection of a mark occursbefore or after the occurrence of said knife position datum signal forthe next preceding mark and for controlling the operation of saidcombining means and said reversible counting means in the appropriateone of said long-size mode and said short-size mode. .Iaddend..Iadd. 8.A control system for controlling the cutting of a web at pointsaccording to preapplied marks thereon by means of a rotary, cutterdriven by a motor, comprising: (a) a first sensor for detecting marks onthe web at which the web is to be cut and giving a mark detectionsignal; (b) a second sensor for establishing a knife position datumsignal during each cutting cycle, the distance between consecutive marksbeing smaller than the distance between said first sensor and saidsecond sensor, the latter distance being a distance from said firstsensor and measured along the path of the web and around the sweptcircumference of the cutter to a position which lies in the range fromthe cutting point to a point spaced around the swept circumference ofthe cutter from said cutting point; (c) a first transducer means forgenerating pulses, the number thereof being proportional to the lengthof the web which has been fed; (d) a signal generator means forgenerating a signal proportional to the web speed; (e) a secondtransducer means for generating pulses, the number thereof beingproportional to the angle through which said rotary cutter has rotated;(f) a first means for providing a first reference value, the magnitudethereof being related to the swept circumference of said rotary cutter;(g) a second means for providing a second value, the magnitude thereofbeing determined by the distance between the mark detection point andthe knife position datum detection point; (h) a combining means forcombining said first value, said second value and a value correspondingto the length of web which has been fed from the instant of detection bysaid first sensor to the occurrence of the knife position datum signalfor obtaining the difference between the first and second values reducedby said value corresponding to the length of fed web to obtain a thirdvalue; (i) a reversible counting means which on generation of each datumsignal by said second sensor receives said third value and which alsoreceives pulses from said second transducer means as a signal to beadded and pulses from said first transducer means as a signal to besubtracted to achieve a resultant count and producing a signalproportional to said resultant count; (j) a differencing means forobtaining a signal proportional to any difference between said signalproportional to said resultant count and said signal proportional to theweb speed; and (k) motor control means responsive to the signal fromsaid differencing means for controlling the operation of said motor tocut the web on said marks.